Globally, tuberculosis (TB) is the leading infectious cause of death among individuals co-infected with the human immunodeficiency virus (HIV). HIV infection is the greatest single risk factor known for progression from TB infection to active TB disease: in developing countries, as many as 40-80% of individuals with the acquired immunodeficiency syndrome (AIDS) will also develop TB. Conversely, co-infected patients with active TB show enhanced viral replication and accelerated progression of AIDS. TB is also the only common opportunistic infection of AIDS patients that is readily transmitted to HIV-positive and HIV-negative contacts. Although TB is a treatable disease, current chemotherapy regimens require administration of multiple drugs for six to nine months. Such prolonged therapy is necessary because conventional drugs are poorly effective against a sub- population of latent and drug tolerant bacterial "persisters". Unless supervised closely, most patients will not adhere to the treatment regimen. Patients who default are at risk for treatment failure, relapse, persisters are ungently needed to counter the problem of patient non-adherence. Development of anti-persister drugs would be facilitated by the identification of bacterial "persistence factors" as candidate drug targets. A significant step towards this goal was our recent demonstration that the glyoxylate shunt enzyme isocitrate lyase is essential for the long-term persistence of Mycobacterium tuberculosis in vivo. Building on this observation, we will take a molecular genetic approach to elucidate the role of fatty acid catabolism pathways in mycobacterial persistence. We will also use signature-tagged mutagenesis (STM) to identify additional persistence factors. In parallel with our animal experiments, David Russell will analyze these mutants in an ex vivo macrophage infection model; he will also carry out a detailed biochemical analysis of the appropriate enzymes when this is feasible. Jim Sacchettini will crystalize the appropriate enzymes for X-ray crystallographic analysis. our collaborators at Glaxo Wellcome (LED BY Ken Duncan) will use this information to guide the development of chemical inhibitors that target persistence factors. Promising lead compounds identified by Glaxo Wellcome will be tested for safety and efficacy in a mouse model of chemotherapy, latency and relapse. The overarching goal of this proposal is to develop new and more effective chemotherapeutics for the treatment of human TB.